For different purposes, it has been known for a long time to situate one or more electric machines in or on a transmission. The applications are basically divided in two groups: 1) the electric machine or machines can perform the tasks of electromotive actuators for shifting transmission gears, thus effecting the torque flow through the transmission without feeding even one torque to a shaft, and 2) one or more electric machines in a transmission can feed a torque to a transmission shaft and/or receive it from a transmission shaft by a generative operation.
DE 101 33 695 A1 and US 2002/033059 A1 disclose dual-clutch transmissions having an integrated electric machine available, which can be located at different points in the transmission, but always acting upon an input shaft. The publications have disclosed multiple different developments and a number of possible manners of using the electric machine. The possible synchronization of transmission elements for the shifting of gears, for example, is actuated by the electric machine. Likewise proposed are possible modes of cold starting and of hot starting of an internal combustion engine connected with the transmission, the same as the recovery of electric energy by a generator operation of the electric machine. For the purpose, the electric machine, existing in the transmission, is energized with torque from the internal combustion engine, one other electric motor or also by the energy of a rolling vehicle.
It is further mentioned that the power of an electric motor existing in the transmission can be used for working together with the prime mover, situated outside the transmission thus to increase the maximum power that can be called for, and the maximum torque that can be called for. It finally says that the electric motor, existing in the transmission, can also be used as an alternative drive whereby the possibility of travel results without participation of the internal combustion engine or any other main engine existing outside of the transmission. However, both DE 101 33 695A1 and US 2002/033059 A1 refer exclusively to dual-clutch transmissions in which at least one gear can be automatically shifted by way of at least one actuator. No suggestions are made for dual-clutch transmission which offer the possibility of entirely manual shifting without using an actuator for automatically shifting or for dual-clutch transmissions which entirely serve the purpose without structurally providing an actuator for automatic shifting. The different alternatives of the embodiments disclosed in DE 101 33 695 A1 and US 2002/0033059 A1 further have in common an electric machine provided in the transmission always acts upon an input shaft or that at least one transmission input shaft is always connectable with the electric machine. Although different structures are proposed in which the electric machine is not directly on an input shaft of the transmission and also does not act directly thereupon, the electromotively applied torque is ultimately always transmitted to the transmission input shaft or received by it in case of generative operation of the electric machine.
Certain disadvantages result from this in relation to maximum possible efficiency. In a vehicle in the gliding operation, that is, during a power-off propulsion phase, when kinetic energy of the vehicle is received via the wheels thereof and introduced in the transmission, it was worth the effort already to receive the power as soon as possible, for example, in the area of the transmission output shaft and not to pass it through the whole transmission subject to losses. In addition, it would be desirable if the clutches could be shifted so that, for example, in case of recovery of electric energy during rolling of the vehicle, the shafts are not needed for the torque flow from the wheels of the vehicle to the electric machine or machines, are not actuated and, accordingly cause little or no power loss. But this is not possible, according to the prior art, since the electric motor or generator always acts upon one input shaft of the transmission.
Together with the stated problem of an improved arrangement of one or more electric machines in a mechanical transmission for reducing the power losses in relation to certain modes of operation and of employment of the motor or motors, it is to be taken into account that for the spatial layout of a vehicle, a transmission is a critical part on which are placed a number of requirements relative to weight, gravity center, geometry, location, number and intensity of the heat-generating components and others.
With this background, it is desirable to find new possibilities for spatial integration of one or more electric machines in one transmission. This is all the more so in the case of a dual-clutch transmission, since the transmissions are often provided for utilizations which place specially high requirements on the operation, the reliability and the degree of efficiency of the transmission. Besides, in their original form without integrated electric machines, dual-clutch transmissions often tend to have a great weight and volume compared to other types of transmissions.
Within the scope of this application, and insofar as not expressly defined otherwise, the expression “electric machines” always comprise those electric machines which can be electromotively and generatively operated.
Special structures of dual-clutch transmissions have already been developed which reduce the installation space required in the sense that several shafts, having similar functions, are locally integrated. At least one hollow shaft is provided for the purpose in which a solid shaft is rotatably supported. This structure offers considerable advantages also in relation to the needed installation space of the dual clutch, since a separately controllable introduction of torque in both transmission input shafts is possible without interposing additional transmission elements for distributing the torque among different shafts. Moreover, both clutches of the dual-clutch transmission can be integrated in the smallest space in an advantageous and a space-saving manner. In addition, if several countershafts, preferably two, are likewise spatially integrated with one countershaft being designed as a hollow shaft in which one countershaft designed as a solid shaft is rotatably supported, especially a small transmission having comparatively several ratio steps are possible which, in many cases, permit the use of dual-clutch transmissions and the utilization of specific advantages thereof.
Precisely in the multi-gear transmission optimized with regard to installation space and weight with several hollow shafts each of which accommodates rotatably supported solid shafts, it is of special advantage if by special forms of the integration of electric machines in the transmission, new possible applications are created which allow equipment of the transmissions with electric machines even in extensively limited or preset installation spaces and also allow, when possible, another efficiency-optimized employment of the electric machines.
With this background, the problem on which the invention is based is to propose new possibilities for integrating electric machines in extensively integrated dual-clutch transmissions in order to disclose new fields of employment for such aggregate combinations under limiting conditions of installation space. Moreover, by adequate arrangement of the electric machine or machines, there is obtained an improvement of the efficiency of the electric machines at least relative to certain possible applications of the same.